ci: attempt to fix platform tag to only the proper platform itself

Author: morpheu

.github/workflows/ci.yaml

@@ -57,10 +57,10 @@ jobs:
     - run: |
         ref="${GITHUB_REF##*/}"
         img="tsuru/${{ matrix.platform }}"
-        tags="${img}:${ref}"
+        tags=""
         if [[ ${ref} == "master" ]] || [[ ${ref} == "main" ]]; then
           tags="${img}:latest"
-        elif [[ ${ref} =~ ${{ matrix.platform }}-([0-9.]+) ]]; then
+        elif [[ ${ref} =~ ^${{ matrix.platform }}-([0-9.]+)$ ]]; then
           tags=${img}:${BASH_REMATCH[1]},${img}:latest
         fi
         echo "::set-output name=tag::${tags}"